PROJECT ABSTRACT The proposed study requests funding to conduct a detailed comparison of eligibility for healthcare coverage and healthcare service use in the Medicaid system among adolescents with autism spectrum disorder (ASD) as they age into adulthood. Given the recent increased number of adolescents diagnosed with ASD, the lifelong presentation of ASD, and the under-researched changes in the needs of adolescents with ASD as they age, examining healthcare access and service use among adolescents with ASD as they transition into adulthood is critical to developing an efficient and effective system of care. Most states have mechanisms to utilize Medicaid to pay for healthcare for a similar group (adolescents with intellectual disability, or ID) as they age into adulthood but it remains unclear if or how these mechanisms also support aging adolescents with ASD. We propose to use 2006-2014 national Medicaid claims data to identify individuals with ASD between 14 and 18 years of age in 2006 who were followed until they were 22 to 26 years of age in 2014. Specifically, we will compare Medicaid eligibility among adolescents with ASD, including the extent to which they remain eligible for Medicaid-funded services into adulthood compared with adolescents with ID. Differences across states with ASD-specific programs, those that serve individuals with ASD through programs established for ID, and states with no programs will be compared. Many states created new programs during the study period, which will be catalogued to measure impact on adolescents with ASD aging into adulthood. We will also examine differences across states in changes in type and quantity of ambulatory, inpatient and residential services among Medicaid-eligible adolescents with ASD and adolescents with ID as they age into adulthood. Interviews with administrators and advocates in states with the most and least discrepant differences in enrollment and service use for adolescents with ASD and ID will also be conducted. Completion of this study will provide a foundation for how differing state approaches to establishing Medicaid programs impact adolescents with ASD during the transition into adulthood.